Bioadhesion is the property whereby some hydrogels adhere to biological tissues, in particular to mucous-coated epithelia such as the gastric, buccal, vaginal and rectal mucosae.
This property has been exploited to develop drug delivery systems, especially in order to increase the time over which drugs remain in contact with certain sites or areas of therapeutic interest, giving rise to systemic effects (thus increasing transmucosal absorption) or local effects.
The most commonly used polymers that are capable of forming hydrogels and imparting bio- and/or muco-adhesion are acrylic or methacrylic acid polymers, possibly cross-linked, and chitosan, or its derivatives.
In particular, for drugs designed for gynaecological use, a bioadhesive gel able to ensure prolonged contact between the active ingredient and the vaginal mucosa, and gradual release of that ingredient over time, provides the ideal solution in terms of efficacy and compliance by patients.
Bioadhesive vaginal gels have consequently been disclosed, for example, in U.S. Pat. No. 6,159,491, US 2002012674, US 2003091642, WO 200047144, WO 200203896, WO 200143720 and WO 9610989. In all these cases, an acrylic acid polymer (Carbomer or polycarbophil) is used as viscosity-controlling or bioadhesive agent.
WO 200015192 describes mucoadhesive formulations in which chitosan is used instead of the acrylic acid polymer.
However, the problem of obtaining a bioadhesive formulation that presents the following advantages and properties:                release of drug for up to approximately 24 hours;        absence of gelling/bioadhesive agents, characterised by the presence of acid groups, which are therefore sensitive to the ionic strength of the medium, and sometimes need to be neutralised with bases;        the possibility of carrying drugs with different chemico-physical properties, in particular water-soluble drugs and lipophilic drugs which are substantially insoluble in water;        reduction of the time and cost of the treatmentremains substantially unsolved.        